Patent GB-1212405-A (GB)
Title: Device for making information visible on the screen of a cathode-ray tube
IPC: G09G1/10
Filed: 1968-03-13
Abstract: 1,212,405. Cathode - ray tube displays. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. 13 March, 1968 [16 March, 1967], No. 12243/68. Heading H4T. In an arrangement for displaying the positions of moving objects (e.g. aircraft located by a radar installation) by respective dots on the screen of a cathode-ray tube, a portion of the total display may be selected and reproduced on an enlarged scale. The selected portion is defined by a mask which may be traced on the screen by the electron beam and the position of which may be adjusted under manual control. Alternatively, the mask may comprise a stencil adjustably positioned in front of the tube screen and in either case the mask may take the shape of a polygonal figure or it may comprise a circle. Additionally, the mask may have different sizes depending on the degree of enlargement required. In the described embodiment the mask comprises a hexagon M (Fig. 1) which is traced on the screen by deflecting the tube beam under the control of digital signals which specify the X, Y co-ordinates of the apices with respect to a reference frame having its origin at A. These digital signals are contained in a store SP (Fig. 5) which also contains the X, Y coordinates of target echoes (aircraft) represented by dots B and C, specified with respect to a reference frame having its origin at O. In operation, the mask co-ordinate binary signals in the form of differences between the starting points and end points of the lines forming the mask together with binary signals (Œ) indicating the algebraic operation to be performed on successive co-ordinate signals and further including binary signals HD indicating the traces which must be blanked, e.g. the run from origin A to the first apex hexagon, are derived from store register SR and supplied via gate UT1 to a difference register DR. Also, the co-ordinates of the dots B and C comprising, for each dot, nine bit binary signals are derived from the register SR and supplied via gate UT2 to the least significant stages of a twelve-stage display register BR formed as a shift register. For manual control of the position of the mask a manually operated, known, " rolling-ball " ROK, operating on the photo-electric principle controls a pulse generator RKST which steps a co-ordinate register KR in either the forward or reverse direction to set-up therein the coordinates of the desired position of the mask origin A. The outputs of registers BR and KR are then supplied via respective gates ST2, ST3 to a add-subtract circuit AS in which the coordinates of the mask reference position A are subtracted serially from the co-ordinates of the dots B and C under the control of timing pulses and the result of this subtraction is entered serially in register BR via the most significant stage. When all nine bits have been entered in the nine most significant positions the timing pulses continue to shift the bits towards the least significant end. For the actual display the contents of register BR are transferred via gate UT3 to a register UR and thence via a digital-toanalogue converter D/A to control the deflection means of the display tube and by opening gate UT3 on the occurrence of the second or third timing (shift) pulse after register BR has been fully loaded the output " number " transferred to register UR is the number which BR would contain if the bits extended from the least significant stage multiplied by the factor 4 or the factor 2 respectively. Thus, the co-ordinates of the dots B and C are expanded by one of the latter factors and after conversion to analogue form in converter D/A the co-ordinate values are utilized to produce the display of the dots on the display tube. Alpha-Numeric characters identifying the different dots are derived from the store SP and fed via the register SR to the converter D/A so that these characters are displayed without enlargement. Fig. 2 shows the result of enlarg. ing the mask M of Fig. 1, by a factor of 2 and Figs. 3 and 4 show the use of two masks with different degrees of enlargement. When the masks comprise stencils (instead of being traced by the tube beam), the stencils are displaceable in front of the tube screen by means controlled by the operator which also control the contents of the co-ordinate register KR by means of an analogue-to-digital converter.